*3.1. Structure and Chemical Composition of DLCs*

Figure 5 shows SEM images of cross-sections of carbide samples with one-layer and double-layer DLCs. The presented photographs give a general idea of the structure of the investigated coatings and the thickness of their layers formed under the selected combination of technological modes. The thickness of the formed adhesive sublayer (CrAlSi)N was 1.4 ± 0.15 μm, and the thickness of the outer DLC layer was 2.6 ± 0.2 μm.

**Figure 5.** SEM images in secondary electrons of cross-sections of carbide samples, high voltage of 10.0 kV, view field of 16.6 μm, 25.0 k×: (**a**) single-layer DLC; (**b**) double-layer DLC.

Tables 4 and 5 present data for processing and decoding the results of XPS analysis of two types of samples with DLCs without sublayer (Table 4) and with sublayer (CrAlSi)N (Table 5). These results were obtained using specialized software of K-alpha X-ray photoelectron spectrometer, an Avantage Data System (version 5.0) (Thermo Scientific, Bremen, Germany). The analysis was performed after the surface layer of the coating with a thickness of about 0.004 μm was etched with argon ions.


**Table 4.** Results of XPS-analysis software interpretation: composition and energy characteristics of DLC peaks (without sublayer).

**Table 5.** Results of f-analysis software interpretation: composition and energy characteristics of DLC peaks (with (CrAlSi)N sublayer).


It should be noted that the binding energies of the coating components are very close for both coatings. The electron energy spectra of the primary coating peak (C1*s*) indicate that in the studied DLCs chemical bonds prevail between carbon atoms with a binding energy of about 284–285 eV, representing *sp*2- and *sp*3-hybridized states. The percentage of the diamond component (*sp*<sup>3</sup> hybridization) in coatings for a sample with a DLC without a sublayer is 47%, and 51% for a sample with a sublayer (we emphasize that here we are talking about a pure diamond component). The proportions of graphite-like carbon hybridization (*sp*2) present in the coatings are very similar for the two samples studied, 16% and 15%, respectively. Besides, in the central peak of the C1*s* coating, the analysis revealed the presence of various impurities and contaminants, which is typical for DLC films. The percentage of this component for a sample with a DLC without a sublayer is 24%, and 17% for a sample with a sublayer. According to authoritative scientists' works, when choosing rational modes of deposition of the investigated type of DLCs, the formation of a diamond phase (*sp*<sup>3</sup> hybridization) in the range of 30–50% is characteristic [10,20,24,26]. That is, the results obtained are at the upper limit of the possible range of values.

XPS analysis of DLC films revealed various oxygen forms with increased binding energy values (O1*s* peak), 531.8 eV and 533.5 eV. Both samples contain oxygen in the form of surface adsorbed groups, and the proportion of the oxygen component is approximately the same and is about 9%. The only difference is that in a DLC film deposited on a sublayer (CrAlSi)N, in the primary oxygen peak of O1*s*, another component was found, identified as silicon dioxide SiO2, its proportion is slightly less than 3%. A photoelectron peak of silicon Si 2*p*<sup>3</sup> was also detected when examining the surface of the samples. The proportion of identified silicon compounds (such as Si, Si–N, SiC) for the studied samples was almost identical and amounted to 2.5–3.0%.
